Cutting off or disabling the fuel supply of a stolen vehicle is well known. For example, a very simple system which restricts fuel flow to the engine is the key operated valve in the fuel line shown by Bradley U.S. Pat. No. 4,084,657. McKinnon U.S. Pat. No. 4,107,962 shows the use of a concealed switch which prevents the fuel pump from operating and which times out to cut out the fuel after the vehicle has only been driven a relatively short distance. The Garreto U.S. Pat. No. 4,991,683, as well as Sangster U.S. Pat. No. 3,834,484, both require that a code be entered into the system via a keyboard or key pad; in Garretto if the code is not entered, power is disrupted to either the ignition coil, fuel pump or a fuel flow valve. In Sangster a valve is opened in the fuel line adjacent the carburetor. All of the foregoing systems are "non-passive" in that they require entry of a code or turning of a special key or hidden switch. Thus they are inconvenient to the user. In addition to the non-passive nature, the systems may be defeated with relative ease. For example, in the Bradley patent with the key operated switch, the cable at the end of the switch can be disconnected and manually rotated. In the case of McKinnon, even though the switch is "hidden", if it is found it can easily be operated. If located in the trunk for example, the trunk lid can easily be pried up. In the case of the Sangster coding device, the actual code unit can be opened and readily defeated. Finally, the Garretto disclosure operates by shutting power off to various components; this means the shut off component can be easily hot wired from the battery.